Thermal protective system



Sept. 20;"1932. E. o. SCHWEITZER 1,877,990

THERIAL PROTECTIVE SYSTEI Original Filed Oct. 3. 1929 Patented Sept. 1932 UNITED-STATES PATENT OFFICE;

THERMAL PROTECTIVE SYSTEM Original application flied October 8, 1929, Serial No. 396,976. Divided and thin application filed November 6, 1980. Serial No. 493,710.

This application is a division of my pendin application Serial No. 396,976, filed Octo er 3, 19:29.

The present invention relates, in general,

to protective means for protecting electric svstems and electrical apparatus against overload. \Vhile the present invention is of generalapplication it is particularly concerned with the provision of overload protecting means for electricalapparatus of the kind that may be required to carry large overloads for short periods of time.

In the embodiment of my invention which has been herein shown for illustrative pur- L'i poses, I show an arrangement for protecting a transformer against overheating and to promptly disconnect the same should the overload reach a predetermined amount in excess of the normal current capacity. Ger- 2 tain apparatus which may be connected to the transformer, such as motors or the like, may take a starting current of from two to five times the continuous current carrying capacity of the transformer: --In order to prevent interruption of the transformer circuit when a motor drawing such heavy current is being started it is necessary to employ fuses whose continuous capacit Y is from two to five times the capacity of tie transformer. Transformers are, naturally, not designed to stand even as much as a 50% overload for two or three hours, hence when an overload of 100% is connected to a transformer for any appreciable period of time the transformer burns up since the fuse af fords no protection.

To avoid the destruction of a transformer upon the occurrence of such an overload, on the theory that such overloads are unavoidable, thermometers, semaphorcd thermal indicators, or other indicating devices have been installed in each transformer and an inspector travels the line to see which transformers are running too hot. It is obvious that the inspector can not be at each transformer when an unexpected load is thrown on due to some customer failing to notify the company of his new load. Therefore, thermal indicators can not be relied upon to roduce the desired results. In addition t ermal indicators are of themselves a source of trouble. It is one of the objects of my present invention to provide a. device which will not only function as a fuse or an oil switch upon the occurrence of an overload but which will, in addition, cut off the transformer when the temperature of the oil in the transformer reaches an excessive value, which may be in the neighborhood of to degrees centigrade. This is accomplished in one of the embodiments of my invention by emersing an oil containing bulb in the transformer casing and connecting this bulb so that upon the expansion of the oil in the bulb, due to a rise in temperature of the transformer, there is produced an expansion of a. sylphon or bellows which controls the tripping of a fast acting switch that is connected in circuit with the transformer.

As previously stated, it is customary to provide a fuse in the transformer circuit and that this fuse is arranged to blow at a current value from two to five times the normal current carrying capacity of the transformer. In the form of my invention herein illustrated I arrange the fuse so that the heat generated by the current flowing through the fuse is effective to help bring about an expansion of the expansible bellows to trip the fast acting switch that is connected in circuit with the transformer. The fuse is preferably mounted in the same container with the switch and the whole is immersed in a bath of insulating oil. The fuse is provided with an enclosing casing so that when the fuse blows the products resulting from the arc of the fuse will not contaminate the insulating oil nor the other parts mounted in the container.

The attainment of the above and other objects of the present invention will be apparent from the following specification, taken in conjunction with the accompanying drawings forming'a part thereof.

In the drawing;

Figure 1 is a diagrammatic view of my improved protective system; and

Figure 52 is a diagrammatic view of a portion of a switch that may be used in place of the switch shown in Figure 1.

Reference may now be had to Figure 1 showing'one form of my invention. In this figure I illustrate a manner whereby my improved cut-out may be adapted to interrupt the circuit to a transformer, or any other electrical translating means, when the same tends to overheat, and this regardless of whether or not the overheating is brought about by the flow of an excessive current or is brought about by a defect in the apparatus. In this figure, a fused cut-out is indicated digrammatically at 1. The cut-out comprises a casing 2 within which'the various switching parts are n'iounted, said casing being adapted to be filled. with a suitable insulating and are quenching liquid and provided with a cover indicated at 3. A fuse link 4 is mounted in a chamber 5 of suitable insulating material, the chamber being suitably mounted within the casing 2 and being provided with a tight fitting cover 6. The chamber 5 is filled with an insulating arc extinguishing liquid such as an. carbon tetra-chloride. ether, or the like. This liquid is preferably one having a high emperature co-etficient of expansion. A bellows 7 is mounted within. the casing 12, said bellows being of any approved construction. A communicating connection 8 connects the chamber 5 with the bellows 7, so that upon expansion of the fluid in the chamber 5 the fluid causes the expansion of the bellows 7. The bellows is fixed at its upper end and is provided with an operating member or rod 9 for actuating a switch 10. The switch 10 is of the multiple break type and comprises a number of contacting fingers 11 which are spaced apart by suitable insulation 12 and are adapted to be short circuited by a conducting arm 13 which swings about the pivot point 14. The circuit through the switch extends from the arm 13 through the uppermost contact finger 11 to a conductor 15 The free ends of the fingers 11 may be connected together by means of a suitable resistor so that upon opening of the movement of the contactor arm 13 sections of the resistor are gradually inserted in the circuit to reduce the current flow and when the contacting arm 18 leaves the lowermost contact finger the circuit is broken. If desired, the resistor may be omitted so that as the contact arm 13 leaves the uppermost contact finger 11 butis still in contact with the contact finger below it an arc is established beswitch by tween the two uppermost contact fingers. As the contact arm 13 continues to move, arcs are successively formed between the next fingers, and when the circuit is ultimately broken by the contact arm leaving one of the lower contact fingers 11 there are a number of. series connected small arcs between the respective contact fingers. It is well recog-' nized that a better current tion is obtained by establishing a large munher of small arcs in series than could be obtained by the establislnnent of a single arc of the equivalent length. The arm 16 is integral with the arm 13 but is formed of insulating material rather than of conducting material. A member 17 is provided for reclosing the switch. This member 17 may constitute a spring or it may be a solenoid.

A line conductor 20 which extends to a source of power enters the cut-out 1 and is connected to the fuse link 4. From the fuse link the circuit extends through a conductor 21 to the switch arm 13. thence by way of theuppermost contact finger 11 to a conductor 15 which extends to the primary side of an oil transformer 25.

The opposite line conductor 26 extends from the source of power to the opposite terminal of the prin'iary winding of this transformer. The r-:ccomlary side of the power transformer is indicated at 27. The transformer 25 is of the usual construction and is filled with oil as is customary. It is, of course, understood that the transformer may be filled with a ditl'erent insulating liquid or it may he an air cooled transformer. As is well understood in the art the secondary 27 of the transformer is connected to furnish current to a predetermined load. This load may consist of one or more devices which take an exceedingly heavy current momentarily when starting. For this reason it is necessary for the fuse to he at a capacity of from two to tire times the continuous capacity of the transformer in order to avoid blowing of the fuse due to a rush of current upon starting of the load. Should a customer increase his load so as to overload the transformer by as much as 50% or 100'}? and fail to notify the power company it is obvious that unless some protective means is provided the transformer will burn up since but few transformers are des gned so as to stand such an overload for a prolonged period of time, say from two to three hours.

In the embodiment of the invention herein shown I have provided means for disconnecting the primary side of the transformer when the temperature of the transformer rises above a predetermined value, and this regardless of whether the rise in temperature is due to an overload on the secondary side or due to some detect within the transformer. A bulb 30 containing oil or other insulating liquid of the kind within the casing 5 is 130 interrupting acemersed in the transformer casing, said bulb being connected by means of a thin tube 31 to the receptacle within which the fuse 4 is mounted. The bellows 7, the casing 5, the tube 31 and the bulb 30 are all filled with insulating liquid. Should a small but continuing overload be connected to the system the fuse 4 will heat the oil within the casing 5 thereby forcing the expanding oil into the bellows 7, which expands so that the lower operating member 9 of the bellows actuates the arm 16 of the switch to actuate the switch to open the circuit.

.. into the casing 5 and then into the bellows 7 thereby further expanding the bellows.

till

It is apparentthat should the transformer overheat due to adefect in the transformer and not due to an'overload, the expanding liquid in the bulb 30 will bring about a tripping of the switch 10.

It is obvious that the principles of my invention are applicable to other translating apparatus than oil filled transformers as shown, since it is apparent that the bulb 30 may be located adjacent any part of an electric device which is liable to overheat. Should a very great overload occur the circuit will be instantly interrupted by the blowing of the fuse 4.

\Vhen a fuse blows in oil or other insulating liquid it spoils the liquid and it also coates the inside of the receptable and everything else around it with a carbon coating that breeds trouble. It is for this reason that I mount the fuse in a separate receptacle 5 within the casing. In my improved cut-out the oil within the fuse chamber is a small proportion of the total oil in the casing 2 hence only a small portion of the total oil in the cut-out is spoiled when the fuse blows. However, the oil within the casing 2 is available for cooling the oil within the fuse chamber during the normal operation of the system and during the time that the fuse blows.

Reference may now be had to Figure 2 showing a modified form of switch which may be used in place of the switch shown in the cut-out of Figure 1. This switch comprises a number of leaf springs of current conductat 56. When the springs are unstressed the circuit is open. T he switch is arranged to be closed by a member 9 of insulating material. This switch closing member is the equivalent of the member 9 of Figure 1, being'connected for actuation by the bottom portion of a bellows 7 of Figure 1. When a switch such as is shown in Figure 2 is used in connection with a cut-out such as is shownin Figure 1, the member 9 is arranged to be elevated when the bellows is expanded instead of being lowered as is the case in Figure 1. When the switch is in the closed position the circuit extends from the conductor 21, through the lowermost suhtch spring 50, thence crosswise through all of the switch springs, the switch springs being in contact with one another, thence by way of the uppermost switch spring to the terminal 55 and the conductor l5.

\Vhen the insulating member 9 raised! a slight amount the springs 50 separate slightly thus introducing one or more small arcs in the circuit. Upon further upward movement of the operating member 9 further separation of the springs take place thereby increasing the number of arcs and increasing the size of the arcs. The first are to be formed is formed between the lowermost spring 50 and the terminal 56. Upon further separation of the springs this are is increased in length until the lowermost spring 50 assumes its normal position as shown in the dotted lines. Further upward movement of insulating member 9 causes the second spring from the bottom to separate from the bottommost spring thus drawing another are. When this spring reaches its normal position as is shown by the dotted lines the next spring separates, this drawingstill another arc, and so forth until the current flow through the circuit is interrupted and the arcs go out. The oil or other insulating liquid surrounding the arcs tends to cool them quickly and in addition the leaf springs 50, from which the arcs extend, being good conductors of heat, help to conduct the heat of the are away from thepoint of current interruption thus serving to accelerate the cooling action and tending to quickly deionize the arc and cause its extinguishment.

My invention is not limited to the use of any particular type of switch in the cut-out shown. The switch of Figure-1 is merely illustrative of a switch in general, and any form of switch or fast acting circuit breaker may be controlled by the operating member 9.

In compliance with the requirements of the patent statutes I have herein shown and described and a preferred embodiment of my invention. It is, however, to be understood that the invention is not limited to the precise construction of the embodiments herein shown but is capable of modification, the embodiments herein shown being merely ilthe expansion of the bellows.

2. In combination, a. closed fluid system including an expansible member, means in cluding an electric fuse for heating the fluid in the system, electric switching means actuated by the expansible member upon expansion thereof, and additional means controlled in accordance with the temperature of the apparatus controlled by the switching means for likewise expanding the cxpansible memher.

3. A cut out comprising a casing, switching means mounted therein, an cxpansible member within the casing for actuating the switching means, and means including a fuse inside the casing and other means outside of the casing for forcing fluid into the expansible member for expanding the member to actuate the switching means.

4. A cut out comprising a casing, switching means mounted therein, an expansible member within the casing for actuating the switching means, means including a fuse iiiside the casing and other means outside of the casing for expanding the member to actuate the switching means, and a bath of insulating liquid for the switching means and the expansible member.

5. In combination, an oil switch, a fuse, electric translating means connected in circuit with said switch and fuse and controlled thereby, an expans-ible member for controlling the switch, means for expanding the member responsive to a temperature rise of the fuse, an expansible liquid in the region of the translating means and expanded in accordance with the temperature thereof, and a tube extending from the translating means to the expansible member for transmitting fluid into the expansible member to open the switch upon the expansion of liquid in the region of the translating means.

6. In combination, electric translating means, a switch and a fuse both controlling the circuit of the translating means, a closed fluid system including an expansible memher, said fuse being arranged in heating realt-ionship to said member, said fluid system also including a portion responsive to the temperature of the translating means; and means for actuating the switching means responsive to the expansionof the expansiblc member.

7. In combination a liquid system containing insulating, are quenching liquid, and including an expansible member, a fuse mounted in the liquid, switching means controlled by the expansion of said member, translating means in circuit with the fuse and the switching means, and means for expanding the member responsive to a temperature rise in the translating means.

8. In combination a liquid system containing insulating, arc quenching liquid, and including an expansible member, a fuse mounted in the liquid, switching means controlled by the expansion of said member, said switching means being connected in circuit with the fuse, and means external of the expansible member and independent of the fuse for expanding said member.

9. In combination, a liquid system containing insulating, arc quenching liquid, and including an cxpansible member, a fuse mounted in the liquid, switching means controlled by the expansion of said member, a bath of insulating liquid surrounding the switching means and the first mentioned liquid system, and means external of said bath of insulating liquid for expanding said member.

10. In combination, a bellows, a fuse containing casing wmmunicating therewith, insulating liquid in the bellowsand in the fuse casing. electric translating means, and means for expanding the bellows responsive to a ten'iperature rise of the translating means.

11. The method of protecting electric translating apparatus, which comprises expandin an expansible member in accordance with the current flow to the apparatus, simultaneously expanding the member in ac cordance with the temperature of the up paratus, and interrupting the circuit to the apparatus when the total expansion exceeds a predetermined amount, regardless of the value of the current flowing at the time.

12. In combination with a transformer including windings immersed in a bath of insulating liquid, a cut out controlling the transformer circuit, means at the cut out for controlling the same and including a member actuated by fluid pressure, a fluid containing bulb immersed in the transformer insulating liquid, said bulb being mechanically connected to the fluid pressure actuated member for actuating the same, and additional means at the cut out for actuating the fluid pressure actuated member, said additional means being responsive to current flow at a point in the transformer circuit external of the transformer.

13. In combination with a transformer including windings immersed in a bath of insulating liquid, a cut out controlling the transformer circuit, control means for the cut out comprising a closed fluid system in- 

